There are two types of radiation, ionizing radiation and non-ionizing radiation. Ionizing radiation is currently considered to be a risk of harm to humans and fetuses.
Ionizing radiation mainly refers to X-rays, gamma rays. It is X-rays that we usually use for medical imaging.
Non-ionizing radiation is common in nature, depending on how we define “radiation”, but the human body itself produces radiation. The human body will produce infrared radiation, expressed as a thermal effect, mosquitoes are generated through the body to determine the target of infrared radiation. Cell phones, refrigerators, color TVs, computers, microwave ovens, induction cookers, ultrasound and other radiation generated by these non-ionizing radiation, the performance of the thermal effect. These are considered to have no effect on the human body or the fetus.
The radiation that is medically feared to bring harm to the human body or fetus is “ionizing radiation”, while the social rumor is that “radiation” can have an effect on the human body or fetus. Before this lost a qualification, the concept is confused, which is obviously not scientific.
Microwave ovens and induction cookers can indeed measure the radiation produced, but it is non-ionizing radiation, which is expressed as a thermal effect, so we can use it to heat meals. I have been asked if the camera has radiation? Camera photography uses the principle of optics, and has nothing to do with radiation.
We will focus on the effects of radiation on the fetus and the risk of teratogenicity in medical examinations. The relatively limited data on the effects of radiation on fertility and birth defects come mainly from couples requiring radiation therapy and from Japan after World War II.
The risk and type of malformations caused by radiation exposure in pregnant women is our primary concern. Ionizing radiation from Hiroshima causes microcephaly, mental retardation and growth retardation in fetuses. Severe mental retardation occurs at 16 to 25 weeks of gestation when exposure to radiation exceeds 50 rads. The most common malformation following exposure to high doses of radiation in the uterus is microcephaly.
The fetus in the organogenesis phase (2 to 15 weeks after gestation) is most sensitive to the teratogenic effects of ionizing radiation.
Before embryo implantation (the first 9 days after conception), the embryo is sensitive only to the lethal effects of radiation, i.e., either embryo loss occurs or no side effect embryo survives intact.
Women may be at increased risk of miscarriage when undergoing diagnostic imaging during the period from the “luteal phase of the menstrual cycle” to “before conception is known”. Animal studies have confirmed that low doses of radiation at 5 to 10 rads before embryo implantation can lead to an increased rate of spontaneous abortion.
Continuation of pregnancy is recommended for those exposed to radiation within 14 days of fertilization.
The 4th to 8th week of gestation is a critical period for cataracts, microphthalmia or skeletal defects.
Even in late gestation the central nervous system is the most sensitive organ to ionizing radiation.
Mental and growth retardation and microcephaly may occur at uterine radiation doses above 10 rads during 4 to 25 weeks of gestation.
The risk of developing childhood cancer may persist until delivery.
The chance of increased risk of genetic disease, birth defects, or childhood cancer in the offspring of parents exposed to radiation to the gonads may be small, estimated at 6-20/1rads per 1 million live births, meaning that for every 1rads of radiation exposure, there are 6-20 additional children with childhood cancer per 1 million live births.
The Oxford Survey of Childhood Cancer (OSCC) in the 1980s showed that if the fetal radiation dose exceeds 1 rad in early gestation, the chance of developing cancer in childhood may increase 3.5 times. The incidence of childhood cancer in people who are not exposed to radiation is 0.07% (1/1500), so the chance of developing childhood cancer increases to 0.25% (3.75/1500) after exposure to a radiation dose of 1 rad in early pregnancy, and conversely the chance of not developing childhood cancer if exposed to radiation in early pregnancy is 99.75%.
I know that even with a 99.75% chance that the child will be fine, the parents-to-be are still concerned, especially in China’s current fertility-restricted environment. But if you were a doctor would you advise your patient to have the baby because of this “small” – 0.18% – increase in risk? I think it is necessary to choose the right insurance for your child. It is worth mentioning that the risk of childhood cancer is significantly increased if the pregnant woman smokes].
There is no significant increase in the risk of macrosomia when the intrauterine radiation exposure is less than 5,000 mrads or when the monthly radiation dose is less than 50 mrads.
The National Council on Radiation Protection (NCRP) has set guidelines for occupational radiation limits. The maximum permissible monthly occupational dose limits for radiation workers who are pregnant are extrapolated so that maximum radiation from diagnostic X-rays should not be used as an indication for termination of pregnancy. (See table below for details).
Fetal exposure to radiation at doses of 5rads or higher during organ development should probably be considered a teratogenic risk and termination of pregnancy should be recommended in some cases.
However, all cases of radiation exposure beyond 15 gestational weeks should be continued.
Mean maternal radiation estimates for through diagnostic procedures versus mean fetal radiation estimates
Imaging procedures
Maternal radiation dose (mrads)
Fetal radiation dose (mrads)
Bone
250
0.05
Chest x-ray
20
0.02 to 0.07
Dental
14～290
0.2
Mammography
300(per breast)
7～20
Gallbladder radiograph
5
Femur
200
103～213
Femur + hip
120～300
Abdomen
300～500
100～245
Lumbar spine
500～750
50～400
Thoracic spine
23
11
Cervical spine
12
<0.5
Lumbar-sacral spine
?
640 to 720
Upper gastrointestinal tract
400～600
100～170
Barium enema
800～1500
820～1000
Intravenous pyelogram
800～1500
690～1400
Head CT
3000～7000
<0.5
Chest CT
2000～5000
16～20
CT scan of abdomen
2000～5000
1000～3000
Pelvis measurement
1000～2000
MRI and fetus.
Magnetic resonance imaging (MRI) does not use the principle of imaging with ionizing radiation, just like ultrasound. It is a relatively safe means of examination. However, the potential effects of the strong magnetic fields and electromagnetic radiation generated by MRI are not known with certainty, so the safety of MRI for unborn fetuses has not been established. However, MRI can make it easier to observe complex fetal malformations through multiplanar reconstruction and large-area scanning, and MRI has been used clinically as an adjunct to ultrasound for the diagnosis of fetal brain malformations and for the diagnosis of congenital diaphragmatic hernia.
In conclusion.
Radiation damage to the fetus can be divided into two main types, teratogenic and carcinogenic effects. Teratogenic effects are mainly limited to the time of organ formation, while carcinogenic effects are seen mainly in mid- and late pregnancy. For most imaging tests the risk of fetal malformation, growth and mental retardation, stillbirth or childhood cancer is small. It is important to know that there is a 3-6% background risk of birth defects per healthy woman. According to current knowledge, there is no significant risk of genetic damage with most radiological examinations. Prenatal exposure to diagnostic radiation at any stage of pregnancy is not a legitimate reason to recommend aborting a pregnancy.
There is no increased risk of macromorphism during major organogenesis and at radiation doses not exceeding 5rads. However, the radiation dose to which the pregnant woman, and especially the fetus, is exposed should be minimized. When pregnancy is possible or after, we should avoid unnecessary tests, except when very necessary, or postpone the relevant tests until after 15 weeks of gestation.